Hi I didn't get the inf I wanted. I wanted to clear a doubt. You guys haven't answered me the question as to how the data enters the rom of the 8051 in particular 89C2051. In the data sheet it's written that only a byte can be written into the memory. For eg I consider the statement mov 90h,#20------>001Fh the extreme right denoting the PC addr. We know that a byte can be entered . So how does this statement represent itself in HEX format and can it be represented in a byte